The Obama administration provided details on Wednesday for its program to help homeowners at risk of losing their houses obtain taxpayer-subsidized reductions in their mortgage payments, a program that becomes available immediately.

Administration officials said the program could help three million to four million families avoid foreclosure, and it is expected to cost $75 billion over the next several years.

In theory, there is no limit on the so-called loan-to-value ratio for a modified mortgage. In other words, people are eligible for help even if the value of their house is far less than the outstanding amount of the mortgage, as is the case for about 14 million people who bought houses at the very peak of the market and often put no money down. Administration officials have said, however, that people who owe more than 150 percent of the current market value of their homes will probably have a harder time persuading their lenders to modify the mortgage.

Below is a list of key elements of the plan outlined Wednesday by President Obama that aims to aid as many as 9 million households in fending off foreclosures:

• Allows 4 million–5 million homeowners to refinance via government-sponsored mortgage giants Fannie Mae and Freddie Mac.
• Establishes $75 billion fund to reduce homeowners’ monthly payments.
• Develops uniform rules for loan modifications across the mortgage industry.
• Bolsters Fannie and Freddie by buying more of their shares.
• Allows Fannie and Freddie to hold $900 billion in mortgage-backed securities — a $50 billion increase.

Some homeowners who are underwater on their mortgages and those stuck in high-cost subprime loans could soon be eligible for a lower mortgage rate, according to an Obama administration plan announced on Wednesday.

But those in the mortgage industry say they’re waiting on details to discover exactly what the requirements are for a homeowner to be eligible for the new assistance.

The government also plans on continuing the purchase of mortgage securities backed by Freddie Mac and Fannie Mae to keep mortgage rates down, President Obama said in a speech.